In modern injection systems for internal combustion engines, piezo actuators which essentially consist of a stack of multiple layers of piezo elements are increasingly being used to actuate the injectors. Between the individual piezo layers of the stack are electrode layers enabling the immediately adjacent piezo elements to be electrically contacted. Metallizations which extend over the entire length of the stack are additionally provided on two opposite sides of the stack, the electrode layers being electrically connected alternately to one of the two metallizations. However, the actual electrical contacting of the piezo actuator is via two electrically conductive connection pins between which the piezo stack is disposed, the two connection pins each being separately connected to one of the two metallizations of the piezo stack.
To establish the electrical connection between the connection pins and the metallizations of the piezo stack, the piezo stack is normally inserted together with the connection pins in a multiple mount in which the connection pins are fixed in a predefined position relative to the piezo stack, whereupon an electrically conductive wire is wound around the piezo stack and the connection pins in a large number of turns. After the wire has been wound around the piezo stack and connection pins, the individual turns of the wire are then soldered to the metallization and the connection pins, thereby establishing an electrical connection between the metallizations and the associated connection pins. The remaining wire sections between the opposite-polarity connection pins or metallizations are then severed and removed in order to insulate the latter from one another. Passivation is then applied to the piezo stack and a foil is adhesively attached to the edges of the piezo stack as edge protection. Finally the units consisting of a piezo stack and two connection pins are then removed from the multiple mount and inserted in suitable sleeves for encapsulation.
The disadvantage of this known production method for a piezo actuator is firstly the fact that the individual piezo units have to be removed from the multiple mount and inserted in the associate sleeve for encapsulation, which requires an additional operation.
Moreover, during encapsulation the two connection pins of a piezo unit must be precisely aligned by a separate guide until the potting compound has cured, thereby immovably fixing the connection pins in position.